Kingpost cranes have long been known in the art. See for instance Purdy, GB Patent No. 10730, AD-1894. Pedestal crane systems, in which a crane upper works is rotatably mounted on a pedestal, have gained widespread acceptance in the marine industry. A form of pedestal crane in which a central kingpost is mounted on a pedestal and the upper works is rotatable about the kingpost and is supported, at least in part, on the kingpost is described in U.S. Pat. No. 4,184,600 issued to Goss and this applicant.
Kingpost cranes of the type described in the '600 patent and subsequent patents such as U. S. Pat. Nos. 5,328,040 and 5,310,067 issued to this applicant and U.S. Pat. No. 4,354,606 to applicant and another have gained widespread acceptance in the offshore oil and gas industry. A primary advantage of such kingpost cranes is the safety inherent in their structure. Such kingpost cranes are highly resistant to overturning moments.
Such kingpost cranes include an upperworks rotatably supported on a kingpost. The structure of such kingpost cranes involves vertical separation of radial bearings. Such separation is normally obtained by providing an upper radial bearing at an upper extension of the kingpost and by providing a lower radial bearing near the level of the pedestal.
Kenz GB Patent No. 2177374A discloses a crane supported on a pivot section, the pivot point disposed below an upper radial bearing. The GB '374A disclosure is for a rope luffed crane, luffing being the adjustment of lateral travel of the block or hook by means of angular adjustment of the boom. The disclosure indicates an advantage of the crane to be an ability to raise the pivot section to allow changing of the upper radial bearing. A disadvantage of the '374 crane is that the '374 crane does not provide means for inspection or replacement of lower radial and thrust bearings without substantial disassembly of the crane. A further disadvantage of the '374A crane is that the lower bearing, like the bearings of many prior art cranes, involves bearing contact of relatively hard metal bearing members with the relatively soft metal of the pivot member. A bearing failure can result in cutting of the pivot member, possibly resulting in overturn of the crane.
It is an object of the present invention to provide a novel kingpost crane having an inverted kingpost.
It is a further object of the present invention to provide an inverted kingpost crane providing upper and lower bearings constructed of relatively soft bearing materials cooperating in bearing relationship with relatively hard kingpost and upperworks structures.
It is a further object of the present invention to provide an inverted kingpost crane providing ready access to upper and lower bearings for inspection and replacement.